This invention relates to the loading of nuclear fuel pellets into a nuclear fuel element and particularly to the automatic loading of fuel pellets from within a sealed compartment.
In many nuclear reactor designs, the reactor vessel has an inlet and an outlet for circulation of a coolant in heat transfer relationship with a core contained therein that produces heat. The core comprises an array or arrays of fuel assemblies which contain fuel elements. The fuel element is generally a cylindrical metallic sheath sealed at both ends containing nuclear fuel. The nuclear fuel which may be, for example, short cylindrical ceramic fuel pellets of a uranium compound is stacked in the fuel elements. During reactor operation, the nuclear fuel fissions thereby releasing fission products such as fission gas while generating heat in a manner well known in the art. The reactor coolant absorbs the heat while circulating through the core thereby cooling the fuel elements of the core and heating the coolant. Of course, the heated coolant may then be used to produce power in a conventional manner.
There are several methods known in the art for loading uranium fuel pellets into the cylindrical metallic sheath for use in a light water reactor. One such method comprises simply placing the fuel pellets in the metallic sheath by hand. Another known method involves placing corrugated metal trays with rows of fuel pellets thereon into alignment with several open fuel elements. Once in this position, the metal trays are vibrated while a person pushes on the ends of the rows of fuel pellets with a device that resembles a large comb, thereby causing several rows of pellets to be loaded into several fuel elements. These methods are possible because nonirradiated uranium fuel does not pose serious radiological problems to working personnel. However, when the nuclear fuel utilized is of a more toxic nature such as plutonium or a reprocessed uranium compound, then increased safeguards must be employed to prevent releasing radioactive contaminants to the atmosphere and to prevent overexposing working personnel. When such toxic fuel is employed, it is known in the art to use glove box handling techniques to hand load fuel pellets into individual fuel elements.
Typical manual glove box handling procedure first requires transferring the nuclear fuel pellets in a sealed container into the glove box and then firmly sealing the glove box. Once placed in the glove box, the sealed container may then be opened by manual gloved manipulation. The fuel pellets may then be loaded into a metallic sheath either totally enclosed within the glove box, or with its open end sealed into a glove box through a plastic membrane. When the metallic sheath has thus been filled to the proper level with fuel pellets, the fuel element must then be placed in a sealed container or its contaminated open end sealed off in order to be moved to the next glove box where the next procedure can be performed such as welding the end plug on the metallic sheath.
An example of an arrangement for mechanically loading nuclear fuel pellets into a fuel element is described in U.S. Pat. No. 3,746,190 to K. Hotz, issued July 17, 1973. The Hotz patent discloses the use of a magazine of nuclear fuel pellets contained within a gas-tight enclosure with a fuel element attached to the enclosure so that a motor driven bead chain mounted therein may push the pellet stack into the fuel element until the pellet stack comes into contact with the end plug at the end of the fuel element. While the Hotz patent does describe one way to load fule pellets into nuclear fuel elements, it does not teach a method to measure and control the amount of fuel pellets loaded into the fuel element.